The reason why the dispensaries across the entire state of California have not been shut down has nothing to do with their being in compliance with state law, because under Mentch, they are not. Instead, it has everything to do with the lack of political will to want to actually do it.
It goes beyond just political will; the fact is that the DEA (even the DEA and state law enforcement combined) don't have the manpower to keep losing this fight. Every year another state adopts mmj laws. Illinois and Arizona appear to be next... definitely Arizona in 2010. We are quickly approaching 50% of the states having mmj laws. In fact, in terms of population, we may already be at 50%.
Every state law that supports medical use increases the magnitude of the job the feds have to perform if they want to actively pursue cannabis users/growers. At some point, they will give up. We may be nearing that point.